1. Technical Field
The present invention relates generally to wireless communication systems; and more particularly to a Time Division Multiple Access (TDMA) wireless communication system that supports packet data transmissions as well as voice communications. In this wireless system, TDMA radio frequency (RF) channels that support packet data operation can be alterable between three different configurations; a dedicated control only configuration, a combination of control and traffic configuration, and a traffic only configuration. Depending upon the packet data traffic loading within a particular cell and the overall system traffic model, a plurality of packet data channels with different configurations may be dynamically allocated to support packet data communications throughout the system.
2. Related art
Wireless communication systems are well known in the art to facilitate communication between a wireless subscriber unit and other wireless subscriber units as well as between wireless subscriber units and users of wired units, such as those attached to the public switched telephone network. Depending on a particular implementation, a wireless communication system operates according to a communication protocol within a frequency band and on particular RF channels contained within the frequency band. Frequency bands currently in use in North America and around the world for wireless communications include the 800 MHz (cellular) band and the 1900 MHz (PCS) band among others.
Various communication protocols have been developed to standardize wireless communication systems. These communication protocols include, for example, the Advanced Mobile Phone Service (AMPS) standards, the Global Standards for Mobility (GSM), the Code Division Multiple Access (CDMA) and the TDMA standard. These standards provide the technical requirements that form the compatibility standard for cellular and PCS mobile telecommunication systems. These wireless communication systems were initially developed to support voice communications. However, with the advances in digital computers and data networking technologies, and the need to provide wireless data services in mobile environment, it has become advantageous to develop wireless communication systems that also support data communication between mobile data terminals (e.g., portable computers).
Some wireless data communication networks, such as the Cellular Digital Packet Data (CDPD) network, have been developed specifically to service packet data communications using existing 30 kHz analog RF channels. However, CDPD protocol has been developed as a stand-alone infrastructure independent of the existing wireless voice communication networks. Creating a completely separate network for data communication requires great redundancy in resources on the network side and on the subscriber side. The voice/data user has to subscribe to two different services, two different networks, and two sets of equipment. Thus, it is advantageous to retrofit existing wireless communication systems that operate according to a standardized air interface protocol (e.g., TDMA) to support packet data communications and provide both services using a single subscriber unit. However, retrofitting existing wireless communication systems to support both voice and packet data communications is difficult, especially considering the different networking protocols and different traffic patterns for packet data communication as compared to voice communications.
Considering the networking difficulties, the two networks (CDPD network and TDMA network) can have a common interface between the Mobile Switching Center (MSC) and the functionality of the Mobile Data Intermediate System (MD-IS) through a Gateway MSC (GMSC). The GMSC shall provide an interface between the two systems in order to track the Voice/Data terminal roaming between both networks. Considering the different traffic patterns for data services as compared to voice services and its impact on the channel configuration, voice service usually requires a relatively longer holding time for each transaction. Therefore, two channel configurations are used to optimally operate such services. The channel can be configured as a control channel, or as a voice traffic channel. The control channel (DCCH) handles paging, registration, access requests, access response, and channel assignment activities. Also, DCCH can handle some Short Message Services (SMS) Control messages sent over the control channel configuration are usually short and bursty while voice conversations which always takes place over the traffic channel have extended channel utilization. Mobile stations initiate calls on the DCCH and thereafter assigned to a traffic channel for the duration of the call. This particular channel configuration allows for the control channel to have enough bandwidth to continue serving the existing population of idle mobile stations while the traffic channel is busy providing a dedicated communication link.
Similar channel configuration can be useful in certain cases of packet data communication systems. However, similar to the nature of voice services this Control-Only and Traffic Only (COTO) channel configurations are most suitable for longer holding time, where the traffic channel is usually occupied for relatively long period of time (e.g., 60-90 sec). This COTO channel configuration would be optimal in case of transferring large data files. Also, it would be best suited for higher traffic areas where a control only channel is needed to handle the excessive number of new arrivals.
However, in case of low-to-medium traffic areas and/or short and bursty data traffic environments, the optimal solution is a channel configuration that can provide control functionality and traffic facilities. In existing systems, both traffic patterns exist and one channel configuration is usually not the optimal solution all the time.
Thus, there exists a need in the art for a wireless communication systems that efficiently allocates resources to optimally support packet data communications, that compensates for expansion and contraction of packet data traffic loading and that may be easily deployed within existing wireless communication system that supports voice communications.
Thus, in order to overcome the shortcomings related to CDPD communication system described above, as well as other shortcomings and limitation of the fixed channel configuration scheme depicted in typical wireless communication systems, a TDMA communication system constructed according to the present invention efficiently services both voice and data communications by configuring and reconfiguring data channels in response to subscriber loading characteristics. The system includes at least one base station that supports the TDMA voice and data communication services on a plurality of RF channels. At least one of these plurality of TDMA channels is a packet data channel that supports TDMA packet data transmissions. According to the present invention, the TDMA channels can be used either for voice or for data purposes. Furthermore, the TDMA packet data channel is alterable between a packet control only channel configuration, packet control and traffic channel configuration, and a packet traffic channel configuration.
When configured in the control only channel configuration, the packet data channel provides control functions, such as paging, registration, access requests, access response, and channel assignment, and facilities for random based access. When in the control and traffic channel configuration, the packet data channel provides control functions as well as traffic (data transfer) facilities. Both random and reservation based accesses are allowed in this mode of operation. When in traffic only configuration, the packet data channel provides traffic only functions (reservation based access). In system deployment, control only channel configuration requires at least an additional packet control channel operating in traffic only channel configuration. However, traffic only configuration can operate with either control only channel configuration, or control and traffic channel configuration. The control and traffic channel configuration can operate as the minimum requirement for initial deployment of packet data systems. Multiple packet data channels can operate independently using the control and traffic channel configurations.
Several deployment scenarios are feasible for packet data systems. Based on the data traffic model, one can decide the optimal deployment scenario. For the initial deployment, where packet data traffic is expected to be light, the control and traffic channel configuration is the optimal scenario. As traffic loads increases, additional channels of the same configuration can be added where the N channels can operate either independently or collectively. Also, the channel configuration of the packet data channel can dynamically adjusted to any valid deployment scenario. Valid deployment scenarios include (1) one control only channel and N traffic only channels; (2) one control and traffic channel and N traffic only channels; (3) N control and traffic channels; and (4) N control and traffic channels and M traffic only channel, where N and M are greater then zero.
Based on the message size and the initial channel configuration, the Medium Access Controller (MAC) of the packet control channel can decide whether to allow the data terminal to continue its transmission on the same TDMA packet channel or to off-load the terminal into a packet traffic only channel. This functionality allows for the optimal deployment of the TDMA packet data system. Also, allocating and configuring multiple packet channels allows the resident system to be expanded to service data traffic as it increases within the system. Further, deallocating packet channels when packet traffic decreases allows valuable system resources to be conserved.
A typical construction of the system would include multiple base stations coupled by a network infrastructure. A network infrastructure in the typical construction would include the functions of CDPD network entities such as base station controller that couples the radio to at least one switching center. The switching center may then couple to one or more data networks, and one or more voice networks. The data networks may support packet data transmissions between data terminals coupled to the system and data terminals coupled to the data networks. One such data network that may be coupled to the switching center is the Internet.
In TDMA systems supporting packet data operation, a subscriber unit has no prior knowledge of the configuration of the packet channel supported by the system. Thus, the subscriber unit listens to the broadcast channel (BCCH) on the Digital Control Channel (DCCH) supported by the TDMA voice system. The broadcast information includes the availability of the packet data services and includes the location of the Beacon Packet Control Channel (PCCH). Upon receiving this information, the subscriber unit tunes to, and listens to the broadcast information on the Beacon PCCH which contains information on the number and the locations of the packet data control channels. Based on this information, the subscriber unit initiates its packet data hatching operation within the system and start listening to a particular packet data control channel. When the packet data channel (system) is reconfigured, the broadcast information on the Beacon PCCH as well as the other PCCH are altered and the subscriber unit may obtain the new configuration from the Beacon PCCH.
As system loading and packet data transmission requirements change, the system may reallocate resources that service packet data communications. For example, during increased loading periods, additional packet data channels may be allocated for data traffic purposes. Of these, one or two packet channels may be used for control purposes while the rest of the channels may be configured for traffic only. Further, as packet data loading decreases or when reallocation is required for other system conditions, packet data channels may be de-allocated and/or reconfigured considering the changes in system conditions.
Moreover, other aspects of the present invention will become apparent with further reference to the drawings and specifications which follow.